1. Technical Field
The present invention relates to masks for manufacturing semiconductor devices that are used in a lithography step in a process for manufacturing semiconductor devices, and manufacturing methods and exposure methods for the same.
2. Discussion
In a photolithography step, one mask is normally used to perform an exposure of one exposure pattern. In the world of photolithography, miniaturization of semiconductor elements has been advanced until recent years through implementation of lenses of larger apertures (higher NA: larger aperture number of projection lenses) in exposure apparatuses, improvements in resist material, and use of shorter wavelengths for exposure light sources. However, since device miniaturizations have been in demand at a pace faster than these improvements, techniques called super resolving techniques have been in use in recent years.
There is a technique called a deformed illumination method in the super resolving techniques. For example, for exposing dense patterns, a strong annuli illumination (with an illumination distribution having a lower intensity towards the middle than its outer periphery) is used, and for exposing rough patterns, the exposure is conducted with a low "sgr" using a halftone mask. Such techniques are used because they are advantageous in terms of exposure characteristics.
However, such special illumination techniques may involve a phenomenon in which the exposure characteristics substantially vary depending on density or roughness of patterns when the patterns of a size smaller than a wavelength of the exposure light may be printed as a result of the advanced miniaturization. Accordingly, when a single chip contains cells having a low pattern density such as logic cells and cells having a high pattern density such as memory cells mixed with one another, it is difficult in a lithography step to finish the cells having a low pattern density and the cells having a high pattern density at the same time and according to the designed measurements.
This is because proper exposures are different depending on the pattern densities. If the exposure is set for one of the pattern densities such that a resist having those patterns has finished measurements according to the designed measurements, finished measurements of a resist having the other pattern density may substantially differ from the designed measurements, such that no pattern may be resolved, or line widths may become narrower than the desired line widths.
In other words, under an illumination condition that is optimized for the dense patterns, the exposure characteristics for the rough or more separated patterns are extremely deteriorated. On the other hand, under an illumination condition that is optimized for the rough patterns, the exposure characteristics for the dense patterns are extremely deteriorated. Accordingly, an illumination condition cannot be optimized for the patterns having mixed dense and separated patterns. This becomes more significant when the design rules for semiconductor devices become smaller.
The present invention has been made in view of the circumstances described above, and its object is to provide masks for manufacturing semiconductor devices, and fabricating methods and exposure methods for the same, which, when patterns having mixed separated patterns and dense patterns are exposed, provide improved exposure characteristics by conducting multiple exposures under illumination conditions that are optimized for the separated patterns and dense patterns, respectively.
In accordance with the teachings of this invention, a mask for manufacturing a semiconductor device in accordance with the present invention pertains to a mask for manufacturing a semiconductor device, equipped with a first mask having separated patterns and a second mask having dense patterns, wherein the first mask and the second mask are exposed under respectively independent illumination conditions to transfer one set of exposure patterns, the mask for manufacturing a semiconductor device characterized in that:
the first mask includes only isolated patterns wherein adjacent ones thereof do not overlap one another when design data for the exposure patterns is enlarged at a specified magnification, and
The second mask includes only dense patterns wherein adjacent ones thereof overlap one another when the design data for the exposure patterns is enlarged at a specified magnification.
Also, in the mask for manufacturing a semiconductor device in accordance with the present invention, the specified magnification may preferably be 2 times.
A method for fabricating masks for manufacturing a semiconductor device in accordance with the present invention pertains to a method for fabricating masks for manufacturing a semiconductor device, equipped with a first mask having separated patterns and a second mask having dense patterns, wherein the first mask and the second mask are exposed under respectively independent illumination conditions to transfer one set of exposure patterns, the method for fabricating masks for manufacturing a semiconductor device characterized comprising:
enlarging design data for one exposed pattern at a specified magnification,
dividing isolated patterns among the enlarged patterns wherein adjacent ones thereof do not overlap one another from dense patterns among the enlarged patterns wherein adjacent ones thereof overlap one another;
forming only the isolated patterns on a mask substrate by a shutter film to fabricate a first mask, and
forming only the dense patterns on a mask substrate by a shutter film to fabricate a second mask.
A method for fabricating masks for manufacturing a semiconductor device in accordance with the present invention pertains to a method for fabricating masks for manufacturing a semiconductor device, equipped with a first mask having separated patterns and a second mask having dense patterns, wherein the first mask and the second mask are exposed under respectively independent illumination conditions to transfer one set of exposure patterns, the method for fabricating masks for manufacturing a semiconductor device characterized comprising:
forming a mask for fabricating a mask having exposure patterns with separated patterns and dense patterns mixed with one another,
exposing under an illumination condition relevant to the separated patterns using the mask for fabricating a mask as a mask to fabricate a first mask on which separated patterns in a normal size and dense patterns in a size extremely smaller than the normal size are transferred, and
exposing under an illumination condition relevant to the dense patterns using the mask for fabricating a mask as a mask to fabricate a second mask on which dense patterns in the normal size and separated patterns in a size extremely smaller than the normal size are transferred.
Also, in the method for fabricating masks for manufacturing a semiconductor device in accordance with the present invention, the specified magnification may preferably be 2 times.
An exposure method in accordance with the present invention comprises:
a step of preparing a mask for manufacturing a semiconductor device, the mask being equipped with a first mask having separated patterns and a second mask having dense patterns;
a step of setting the first mask in an exposure apparatus, and setting an illumination condition with the exposure apparatus relevant to the separated patterns to perform an exposure using the first mask as a mask; and
a step of setting the second mask in an exposure apparatus, and setting an illumination condition with the exposure apparatus relevant to the dense patterns to perform an exposure using the second mask as a mask,
wherein the first mask includes only isolated patterns wherein adjacent ones thereof do not overlap one another when design data for one set of exposure patterns is enlarged at a specified magnification, and
the second mask includes only dense patterns wherein adjacent ones thereof overlap one another when the design data for the one set of exposure patterns is enlarged at a specified magnification.
According to the exposure methods described above, in a stage where masks for manufacturing semiconductor devices are fabricated, data for separated and dense patterns are divided, two masks therefore are fabricated, and the patterns are transferred through multiple exposures with the divided masks under respectively relevant illumination conditions. As a result, the exposure characteristics can be improved compared to the exposure with one mask such as in the conventional exposure method.
An exposure method in accordance with the present invention comprises:
a step of preparing a mask for manufacturing a semiconductor device, equipped with a first mask having separated patterns and a second mask having dense patterns;
a step of setting the first mask in an exposure apparatus, and setting an illumination condition with the exposure apparatus relevant to the separated patterns to perform an exposure using the first mask as a mask; and
a step of setting the second mask in an exposure apparatus, and setting an illumination condition with the exposure apparatus relevant to the dense patterns to perform an exposure using the second mask as a mask,
wherein a mask for fabricating a mask having exposure patterns with separated patterns and dense patterns mixed with one another is prepared,
the first mask is fabricated by exposing under an illumination condition relevant to the separated patterns using the mask for fabricating a mask as a mask to thereby transfer separated patterns in a normal size and dense patterns in a size extremely smaller than the normal size, and
the second mask is fabricated by exposing under an illumination condition relevant to the dense patterns using the mask for fabricating a mask as a mask to thereby transfer dense patterns in the normal size and separated patterns in a size extremely smaller than the normal size.
Also, in the exposure method in accordance with the present invention, the specified magnification may preferably be 2 times.